Safety device for a portable battery-powered electric apparatus

Abstract

A safety device for a portable battery-powered electric apparatus having a battery unit with one or more battery cells for supplying power to electric circuitry in the apparatus. The apparatus is connectable to a charging device for charging the battery unit while maintaining the supply of power to the apparatus. The safety device has a first fuse device connected between the battery unit and a first terminal of the apparatus for receiving charging current from the charging device, and a second fuse device connected between the battery unit and a second terminal of the apparatus for supplying power to electric circuitry in the apparatus. The fuse devices are operatively independent of each other, particularly in that the second fuse device maintains the electric connection between the battery unit and the electric circuitry in the apparatus, even when or if the first fuse device releases or opens in response to an undesired condition in the charging device.

What is claimed is: 
     
       1. A safety device for a portable battery-powered electric apparatus having a battery unit with at least one battery cell for supplying power to electric circuitry in the apparatus, the electric apparatus being arranged to be connected to a charging device for charging the battery unit while maintaining the supply of power to the electric apparatus, comprising: a first fuse arranged to be connected between the battery unit and a first terminal of the electric apparatus for receiving charging current from the charging device, and   a second fuse arranged to be connected between the battery unit and a second terminal of the electric apparatus for supplying power to electric circuitry in the electric apparatus,   wherein the first and second fuses are operatively independent of each other, particularly in that the second fuse can maintain an electric connection between the battery unit and the electric circuitry in the apparatus even if the first fuse opens in response to an undesired condition in the charging device.   
     
     
       2. The safety device of claim 1, wherein the first and second fuses are physically integrated. 
     
     
       3. The safety device of claim 1, wherein the first and second fuses are formed as layers of a material that is active with respect to at least one physical property, the layers are arranged between a contact tab and a first contact and a second contact, respectively, the contact tab is arranged to be connected to the battery unit, the first contact is arranged to be connected to the first terminal, and the second contact is arranged to be connected to the second terminal. 
     
     
       4. The safety device of claim 3, wherein an electrical conductivity of the material in a direction between the contact tab and the first and second contacts, respectively, is substantially zero when a temperature of the material exceeds a predetermined upper threshold value and returns to a non-zero value when the temperature of the material falls below a predetermined lower threshold value. 
     
     
       5. The safety device of claim 3, wherein the first and second contacts have planar upper surfaces for receiving a respective resilient contact of the electric apparatus. 
     
     
       6. The safety device of claim 5, wherein a third contact is mounted on the contact tab by an intermediate layer of an electrically isolating material, which has a planar upper surface for receiving a third resilient contact of the electric apparatus, and which is arranged to be connected to a negative side of the battery unit while the contact tab is arranged to be connected to a positive side of the battery unit. 
     
     
       7. The safety device of claim 1, wherein the electric apparatus is a mobile telephone for a cellular mobile telephone system. 
     
     
       8. A rechargeable battery unit having at least one battery cell for supplying power to a portable electric apparatus, wherein the battery unit comprises a safety device according to claim 1.